Electric wires or cables may be received and protected by a variety of mechanisms including conduits which are typically insulated at their ends with bushings or other insulating devices to permit compliance with the National Electrical Code (NEC). In particular, the NEC requires that ungrounded conductors of No. 4 or larger be protected from abrasion by a substantial bushing which provides a smooth rounded insulating surface. An exception to this bushing requirement would be the presence of threaded hubs or bosses that are an integral part of the enclosure and which provide a smooth rounded or flared entry for conductors.
Irrespective of the insulating mechanism, conduits are often found entering walls of enclosure and are mounted into the enclosures by one of three methods.
The first method involves mounting a conduit in a knockout or sliphole of an enclosure wherein it may be secured by a single or double locknut. A bushing is screwed or set-screwed into the end of the conduit which protrudes into the enclosure.
The second method entails screwing a conduit into a thin walled enclosure and requires drilling and tapping the opening of the enclosure with a taper tap so that the conduit protrudes into the enclosure. A bushing is fastened to the end of the conduit that protrudes into the enclosure. Alteratively, a reducer may be utilized with the conduit to provide an integral bushing.
The third method involves screwing a conduit into a drilled and taper tapped conduit entry in a thick walled enclosure, such as an explosion-proof enclosure. This method may be accomplished by: employing a reducer with an integral bushing; machining an integral bushing into the enclosure; or counterboring the opening of the enclosure such that the conduit protrudes sufficiently into same and a bushing may be installed on the end of the conduit.
In addition to the above three methods, a fourth method involves using insulating throat liners in conduits. For example, in U.S. Pat. No. 2,947,800 (Badeau), a permanent, factory-installed, tubular liner is placed in the throat of the conduit and cable fittings. The Badeau liner, however, requires an internal recess or flange in the conduit fitting for containment.
While the aforementioned methods and associated products function to provide a conduit with a bushing that complies with the NEC, there are problems associated with their use. For example, the third method generally requires extensive machining operations to form the conduit entry which elevates the cost and delays the completion time. Furthermore, these methods typically require the presence of fittings and internal bushings that are affixed to the ends of the conduits which protrude into the enclosures. Moreover, these methods necessitate mounting the conduits into an enclosure so that bushings may be attached thereto.
Likewise, the fourth method requires a liner which is permanent and factory installed and further requires the presence of a fitting for attachment purposes.
These requirements are also prohibitively costly and time consuming.
Despite the numerous disadvantages and limitations with the above methods and their respective apparatuses, conduits are still generally mounted and insulated as described above. Thus, while these methods and bushings provide a means to insulate and provide smooth conduit entry, they are not adequate to meet the needs of the art. Moreover, these methods and bushings are generally expensive to use and all are restrictive in their use.
Accordingly, it is an object of the present invention to provide a method for producing a smooth conduit entry and a conduit liner having a plurality of flexible collapsible locking fins extending outwardly from the outer surface of the liner.
It is another object of the present invention to provide a method for producing a smooth conduit entry and a conduit liner which may be inserted into the open end of a conduit and the liner having a plurality of integral collapsible locking fins having a thickness of less than 0.03 inches.
It is another object of the present invention to provide a method for producing a smooth conduit entry and a conduit liner which may be inserted into the open end of a conduit that does not have a fitting and said liner having a plurality of their locking fins which collapse when the liner is inserted into the conduit such that one side of the liner contacts the liner outer walls and the other side of the liner contacts the inner walls of the conduit.
Other objects and advantages of the present invention will become more apparent as described hereinafter.